The invention pertains to the field of computer storage and retrieval systems and in particular to a method for adjusting the operating parameters of disk drives by determining the errors in reading and writing signals to the disk drive and then optimizing the parameters for the drive.
A data storage and retrieval system, such as a hard disk drive or a floppy disk drive, is typically the principal memory device in a desktop computer. The technology of memories and disk drives has improved from the days when a single megabyte was considered abundant memory, to the present day in which a hard disk capable of storing many gigabytes is considered standard. In some disk drives, the read/write tracks now approach 100,000 tracks per inch (about 40,000 tracks per cm). Put another way, each track is separated from the next by about 10 millionths of an inch (about 25 millionths of a cm).
One thing that has not changed is the need for this device to store data accurately, and for the disk drive read/write head to xe2x80x9creadxe2x80x9d each byte correctly and to store or xe2x80x9cwritexe2x80x9d each byte correctly. Disk drives must be manufactured and tested to ensure that error rates are within the acceptable range of about 1 in 100 million or less. In order to accurately test for such low error rates, it may take a very long time, up to several minutes, in order to xe2x80x9creadxe2x80x9d or xe2x80x9cwritexe2x80x9d up to 1010 bits and determine an error rate with a sample of at least about 100 errors. This process must be repeated for each parameter tested, and a typical disk drive may have hundreds of parameters that must be optimized and tested.
In order to speed up the process, additive white Gaussian noise (AWGN) may be added to a signal in the readback signal path. This adds errors to the signal and allows faster determination of error rates in the disk drive. However, AWGN is not typical of the interference normally encountered in disk drive service. Therefore, disk drives that are optimized by using AWGN for their channel settings may not have the ideal settings for a xe2x80x9creal-worldxe2x80x9d low error rate. What is needed is a way to speed up the testing and optimization of disk drives by adding an error more realistic and typical of hard disk drive service.
In order to address these deficiencies of the prior art, a disk drive having a magnetic recording channel is tested by adding an interfering signal simulating an error of an adjacent track of the disk drive. In one embodiment, method for testing the magnetic recording channel for a disk drive comprises providing the magnetic recording channel, providing a first signal from the disk drive, and digitizing the signal to a digital output. The method also includes providing a pseudo-random interference signal. The pseudo-random interference signal emulates an error signal produced by the read/write head reading data from an adjacent track rather than from the desired track on the hard disk drive. The interference signal is added to the digital output to provide a second signal. The second signal, including the interference, is sent to a Viterbi detector to determine an error rate.
In another embodiment, a magnetic channel off-track interference emulator for generating a pseudo-random interference signal is discussed. The emulator comprises an analog to digital converter (ADC) that receives an analog signal from a read/write head and converts the signal to a digitized output. The emulator also comprises a linear feedback shift register (LFSR) that generates a pseudo-random binary sequence of numbers, the sequence simulating a signal close to that of an error signal from off-track random data. The emulator also includes a multiplier, the multiplier receiving an output from the LFSR and applying an adjusting factor to form an interference signal. The interference signal and the digitized output of the ADC are sent to an adder to produce a test signal. The emulator also includes a Viterbi detector that detects errors in the test signal and determines an error rate.